Impulsing circuit including a preenergizing circuit for the impulsing relay



Sept. 7, 1948. 2,448,608

IMPULSING CIRCUIT INCLUDING A PREENERGIZING ,CIRCUIT FOR THE IMPULSING RELAY Filed Dec. 13, 1945 2 SheetsSheet 1 INVENTOR. QLARENGE s. LOMAX ATTCRNEY Sept. 7, 1948. g, LQMAX 2,448,608

IMPULSING CIRCUIT INCLUDING A PREENERGIZING CIRCUIT FOR THE IMPULSING RELAY Filed Dec. 13, 1945 2 Sheets-Sheet 2 INVENTOR. G LAR ENGE E LOMAX ATTORNEY Patented Sept. 7, 1948 IMPULSING CIRCUIT INCLUDING A PRE- ENERGIZING CIRCUIT FOR THE IM- PULSING RELAY Clarence E. Lomax, Chicago, 111., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application December 13, 1945, Serial No. 634,770

9 Claims. 1

The present invention relates to improvements in impulsing circuits for switching mechanisms, such as are employed in automatic telephone systems; and particularly to improved lock-pulse impulsing circuits for such switching mechanisms.

One of the most widely known and most commonly used switching mechanisms employed in automatic telephone systems is the so-called Strowger switch, in which a shaft is raised and rotated by a step-by-step mechanism to cause wipers on said shaft to selectively connect with terminals in switching banks to establish electrical connections. The combination of such a switching mechanism and the control relays necessary to direct the operation of the mechanism is generally known as an automatic switch. Such switches are divided into two principal types; namely, selectors and connectors. In selector switches the vertical motion of the shaft is effected under the control of an impulse transmitter, such as a subscribers dial, and the rotary motion of the shaft is automatic. In connector switches both the vertical and rotary motions of the shaft are effected under the control of the impulse transmitter. Both selectors and connectors have heretofore been provided with lock-pulse impulsing circuits to insure satisfactory operation of the stepping mechanism under adverse impulsing conditions, such as long and/or leaky subscriber's lines. In recent years the transmitters employed in subscribers substation sets have been improved to the point where satisfactory Voice transmission is obtained with much lower values of line current than was formerly used. This has resulted in the use of smaller line conductors which has raised the resistance of subscribers lines to the point where impulsing becomes unreliable with ordinary impulsing circuits. The lock-pulse impulsing circuits formerly used enable satisfactory impulsing to be accomplished over high resistance lines but have the disadvantage of requiring additional relays in the switches.

It is accordingly an object of the present invention to provide an improved lock-pulse impulsing circuit for automatic switches of the above described type without the need of additional relays.

A feature of the invention is the provision of a pre-energizin circuit, for the usual line relay of an automatic switch, which is closed a predetermined time interval after each restoration of the line relay and is opened a predetermined time interval after each operation of the line relay, whereby more stable operation of the line relay is secured.

The invention may best be understood from the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a schematic circuit diagram showing the application of the invention to a conventional connector switch;

Fig. 2 is a perspective view showing how special contact assemblies used in the circuit of Fig. 1 may be added to a conventional Strowger switch mechanism;

Figs. 3 through '7 show the sequence of operation of the special contact assemblies shown in Fig. 2;

Fig. 8 is a schematic circuit diagram of a modification of the invention as applied to a conventional connector switch; and

Fig. 9 is a perspective view showing how special contact assemblies used in the circuit of Fig. 8 may be added to a conventional Strowger switch mechanism.

Briefly described, the invention comprises the provision of a special contact assembly, which is operated by a stepping magnet of the switching mechanism, to close a locking circuit to the stepping magnet in response to a partial operation of the armature thereof, to open said locking circuit in response to the complete operation of said armature, and to maintain said locking circuit open during the return movement thereof. Thus, as long as the impulses delivered to the steppin magnet are of sufficient duration to insure closure of the locking circuit, positive operation of the stepping magnet is assured even though the impulses delivered thereto are of insufficient duration to enable complete operation thereof without the locking circuit. In one form of the invention a pro-energizing circuit for the stepping magnet and the usual changeover relay is also controlled by contacts including in the special assemblies operated by the stepping magnets. In the second form of the invention a pro-energizing circuit for the usual line relay is controlled by toggle-action switches operated by the stepping magnets, which toggle-action switches also are used in the lock ing circuits for the stepping magnets.

Referring now to the drawings, in Fig. 2 there is shown a portion of the stepping mechanism of a conventional Strowger switch comprising a vertical armature l, a rotary armature 2, and a pair of rotary magnets 3. The vertical magnets have been omitted for clarity. Reference may be had to Patent 2,340,811, issued to Joseph A. Kater, for various details of the Strowger mechanism not shown herein. The vertical and rotary armatures have been modified by the addition of arms 4 and 5 extending therefrom. The arm 4 extending from the vertical armature I has two insulated pins, 5 and 6, secured to the end thereof, which pins engage armature springs B and 9 when the vertical armature is operated. Similarily, the arm 5 has two insulated pins, II and 12 secured thereto, which pins engage armature springs M and it when the rotary armature is operated. Contact springs l to it and it to It are secured to brackets ii and it, respectively, which are secured to the frame, not shown, of the Strowger switch mechanism. The sequence of operation of contact springs it through is during the operation of the rotary armature 2 has been illustrated in Figs. 3 to 7. \Vhen the rotary armature is normal contact springs E3 and I 4 are open and contact springs l5 and it. are closed, as shown in Fig. 3. In response to a partial operation of armature 2, the pin ii engages armature spring Ill forcing it into engagement with contact spring it, as shown in Fig. 4. In Fig. 5, the arm 5 extending from armature 2 is shown near the end of its stroke where pin 12 is about to engage armature spring 15. During the final movement of the armature 2, pin l2 engages armature spring l5 and forces it away from contact spring it. At the same time, the "pin in passes beyond the extending portion of armature spring is with which it has been enga'ge'd, thus permitting the armature spring it to restore, as shown in Fig. 6. As the armature 2 restores, the pin i2 permits armature spring j I5 to restore and again contact the associated contact spring it, while pin l i returns on the opposite side of the extending portion of armature spring i l forcing it further away from its associated contact spring is, as shown in Fig. 7. When the armature 2 again reaches its normal position the pin ll passes beyond the end of armature spring M permitting it to return to its normal position shown in Fig. 3. The contact springs l to H) are operated in a similar manner when the vertical armature l is operated.

The manner in which these contact assembli-es are employed in a connector switch will now be described with reference to Fig. 1. In this figure there is'shown a calling device it of a subscribers subset, which is connected over line 20 to relay 2! of a connector switch. The usual .line relays and line finder, or the equivalent, may be included between the line 28 and the connector switch, but have been omitted for simplicity. Only that portion of the connector switch which is related to impulsing has been illustrated. When a circuit is completed to line relay 2! over line 28, as by the removal of the receiver from the hookswitch at the subscribers subset, relay 21 operates and closes a circuit to the upper winding of the usual holding relay 23 at contacts 22. Relay 23 operates, prepares a circuit to the vertical magnets 2 in series with the usual changeover relay 25 and normally closed contacts of the vertical oiT-normal springs 26 at contacts 21, and prepares a pre-energizing circuit for the changeover relay 25 and vertical magnets 24 through resistor 23 and the lower winding of relay 23 at contacts 29. When the calling device I9 is operated to-transmit a digit the circuit to relay 2! is interrupted a number of times corresponding to the digit value. The first time that relay 2| restores, in response to the interruption of the circuit thereto, it opens the circuit to the upper winding of relay 23 and closes the previously traced circuit to relay 25 and the vertical magnets 2 at contacts 22. The vertical magnets 24 will quickly operate sufiiciently to close contacts '5 and 8, thereby closing a locking circuit to the vertical magnets through relay 25, since these contacts are adjusted so as to be closed before the pawl secured to the end of the vertical armature I engages the vertical ratchet of the switch shaft, not shown. When this pawl does engage the vertical ratchet the operation of the vertical magnets will be retarded due to the added load of the switch shaft. The locking circuit completed by contacts l and 8 assures the complete operation of the vertical magnets and the continued operation of the changeover relay even though relay H is reoperated before the vertical magnets have had time to complete their operation. Relay operates in response to the first impulse, prepares a circuit to itself and the vertical magnets 24 through the normally open contacts of the vertical off-normal springs 25 at contacts Sll, and further prepares the pre-energizing circuit to itself and magnets 26 at contacts 3!. The vertical off-normal springs are operated when the switch shaft is raised to the first level by the vertical magnets As the vertical armature reaches the end of its stroke contacts l, S and 9, is are opened causing the vertical magnets to restore immediately if relay 2% has been reoperated in the meantime. If relay 2! is still at normal the circuit to magnets 2 remains closed until relay .Zi is reoperated. When magnets 22 irestore contacts 9, it} are reclosed to complete the pre-energizing circuit from ground through contacts 29, the lower winding of relay 23, resister 23, contacts 3i, and contacts 9, so to relay 25 and the vertical magnets 2c in series. The value of resistor 23 is made sufficiently high so as to prevent continued operation of relay 25 in series therewith, but is low enough to assist in holding relays 23 and 25 operated during impulsing and to reduce the operate time of the vertical magnets. Relays 23 and are both provided with copper sleeves to render them slow tion thereof when relay 25 to release. When relay 2i restores the second time it again opens the circuit to the upper winding of relay at contacts 22 and closes a circuit through contacts 27, make contacts of the vertical off-normal springs 25, and contacts 3a to relay 25 and the vertical magnets (l-l in series. The ground extended to relay 25 from contacts 22 also short-circuits the lower winding of relay 23 through resistor 28 and contacts 3i and ii, iii. The vertical magnets 2d again operate quickly to close the locking circuit at contacts l, 8, which circuit is opened in response to the complete operation of the vertical armature and remains open during the return movement thereof. The previously traced pre-energizing circuit is also opened at contacts $3, is in response to the complete operation of the vertical armature in order to insure quick restorarestores. Shortly after the last impulse of the series has been received, relay v25 restores and transfers the impulsing and pro-energizing circuits from the vertical magnets to the rotary magnets 3 at contacts 3B and Si. During the next series of impulses the operating circuit of change-over relay 25 remains open at the vertical off-normal springs 26. The circuit of the rotary magnets 3 is similar to that of the vertical magnets 24 eX- cept that a relay corresponding to changeover relay 25 is not required. Since the preenergization or operation of the magnets is not noticeably effected by the removal from the circuit of a low series resistance as that of changeover relay 25, the next series of impulses operates the rotary magnets 3 in a manner similar to that described for the vertical magnets 25.

In the modified form of the invention disclosed in Figs. 8 and 9 an alternative method of operating the auxiliary contact spring assemblies has been illustrated. In this case each spring assembly comprises five contact springs, namely, 32 to 36 and 3'! to 4|. The normally open contact springs 35, 36 and 49, M are operated by insulated pins 42 and 43 which are secured to the arms 44 and 45 extending from the vertical and rotary armatures 41 and 48, respectively, in response to a partial operation thereof. The

rackets, 49 and 58, to which these contact assemblies are secured, extend to a point adjacent the arms 44 and 45. A toggle mechanism is secured at the end of each of these brackets. Thus at the end of bracket 58, the lever is pivotally secured by a shoulder screw 52. A V-shaped spring 53 has one end pivotally secured to the bracket 59 and has its other end pivotally secured to the lever 5| to impart a toggle-action to the lever 5i. One end of lever 5| has two upstanding ears 54 and 55. An insulated pin 56 extends from the ear 55. When the armature 48 is operated, the pin 43 engages armature spring ii! to force it into contact with spring id in response to a small movement of the armature 48. Near the end of the stroke of armature 6B the tip of arm 5 engages car 55 causing lever 55 to snap from one over-center position to another over-center position. The pin 56 then engages armature spring 38 moving it out of contact with spring 39 and into contact with spring 31. During the return movement of the armature 48 the pin 43 allows armature spring as to restore before the tip of arm 45 engages ear 54 to return lever 5! to its normal position. The toggle mechanism associated with the vertical armature and contact springs 32 and 38 operates in a similar fashion.

Referring now particularly to Fig. 8, when a circuit is completed to line relay 5'5 over line 58 from a subscribers subset including a calling device 58, relay 52 operates and closes a circuit to the usual holding relay 6'! at contacts 6 l. Relay 60 operates and prepares a circuit to the vertical magnets 62 in series with the usual changeover relay 63 and. normally closed contacts of the vertical oiT-normal springs 54 at contacts 55. When the calling device 59 is operated to transmit a digit the circuit to relay 5! is interrupted a number of times corresponding to the value of the digit. The first time that relay 5'! restores in response to the interruption of the circuit thereto it closes the above traced circuit to magnets 62 in series with relay 63 at contacts 5!. The vertical magnets quickly close contacts 35, 38 thereby closing a locking circuit to themselves in series with contacts 33, 34 and relay 63. The closure of this locking circuit insures the complete operation of the vertical magnets and the continued operation of the changeover relay even when relay 5! is restored for only a short interval. Relay 53 operates in response to the first impulse, prepares an alternative impulsing circuit to the magnets 52 through relay 63 and the normally open contacts of the vertical. off-normal springs 64 at contacts 65, and prepares a pre-energizing circuit to relay 5! through resistor 61 at contacts 68. As the ver tical armature nears the end of its stroke the toggle-action contacts 32, 3-3, 34 are operated to open the vertical magnet locking circuit at contacts' 33, 34 and to close the line relay pro-energizing circuit at contacts 32, 33. Resistor G1 has a value suificiently high so as to prevent relay 5'! from operating in series therewith, but sufl'iciently low so as to materially reduce the operate time thereof when the resistance of line 58 is high. When the vertical magnets raise the switch shaft to the first level the vertical offnormal springs 54 are operated to open the original circuit to the vertical magnets and to close the alternative impulsing circuit through contacts 6%. If relay 5'1 is still operated after the vertical magnets have operated completely, the vertical magnets remain energized until relay 5'5 restores. If relay 5'! has previously restored the interruption of the locking circuit to the vertical magnets at contacts 33, 34 deenergizes the magnets c-ausing them to restore. The locking cirouit remains open during the return movement of the vertical armature since the contacts 35, 35 are opened before the toggle-action contacts 2, 33, 34 are restored to normal.

Upon each succeeding restoration of relay 5! a circuit is completed from ground through con tacts 6i and 65, make contacts on the vertical off-normal springs as, and through contacts 66 to relay 63 and vertical magnets 62 in series. The vertical magnets quickly close their locking circuit at contacts 35, 3B and subsequently open the lockin circuit at contacts 33, 34 and close the pro-energizing circuit to relay 5! at contacts 32, The operate time of the vertical magnets is used to delay the closure of the impulsing circuit to the line relay 5! in order to provide more stable operation thereof than would be obtained if t e pre-energizing circuit was completed by break contacts on this relay, as is customary. When the pro-energizing circuit is closed by break contacts on the line relay some instability in the operation thereof is apt to occur due to the fact that the lure-energizing circuit is closed at a time when the flux in the relay core has decayed just enough to permit restoration of the relay armature. The sudden rise in flux produced by the closure of the pro-energizing circuit at that time may be suflicient to partially reoperate the relay and produce chattering of the break contacts. When the closure of the pre-energizing circuit is delayed until the flux in the line relay core has had time to decay to a low value a greater degree of pre-energization may be used without producing unstable operation of the line relay. It should be noted that the opening of the pre-energizing circuit in response to the re-operation of the line relay is delayed by the release time of the vertical magnets, thus avoiding any tendency for the line relay to restore at the instant that the pro-energizing circuit is opened.

Relay 63 restores shortly after the termination of the first series of impulses and transfer the impulsing and pre-energizin circuits to the rotary magnets 69 at contacts 66 and 68. The next series of impulses cause the rotary magnets to be operated in the same manner as described for the vertical magnets.

While particular embodiments of the invention have been illustrated, it is to be understood that numerous modifications in the details of con struction and arrangement of circuits may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In an automatic switch, a stepping magnet having a single armature, a circuit over which a series of impulses are delivered to said magnet, a locking circuit for said magnet, each impulse of a series at times being of insuihcient duration to permit complete operation of said armature, a pair of normally open contacts closed by a partial operation of said armature in response to each of said impulses, said contacts closing said locking circuit to insure the complete operation of said armature, said contacts opened in response to the complete operation. of said armature and remaining open during the restoration thereof, a pair of normally closed contacts opened by the operation of said armature in response to each of said impulses, and a circuit serially including said normally closed contacts over which said magnet is preenergized.

'2. In an automatic switch, an impulsing relay, a slow release relay, a stepping magnet, an operating circuit for said slow release relay including make contacts on said impulsing relay, a pre-energizing circuit for said magnet including make contacts on said slow release relay and break contacts on said magnet, an operating circuit for said magnet including break contacts on said impulsing relay and make contacts on said slow release relay, and a locking circuit for said magnet in--' cluding normally open contacts thereon which are closed in response to a partial operation thereof and opened in response to the complete operation thereof.

3. An automatic switch as claimed in claim 2 wherein said pre-energizin circuit includes a 't inding on said slow release relay to assist in maintainin it operated during impulsing.

i. In an automatic switch, an impulsing relay, a slow release relay, a stepping magnet having a single armature, an operating circuit for said slow release relay including make contacts on said impulsing relay, a Dre-energizing circuit for said magnet including make contacts on said slow release relay and break contacts on said magnet, an operating circuit fo said magnet including break contacts on said impulsing relay and make contacts on said slow release relay, a pair of normally open contacts closed by a partial operation or" said armature in response to each momentary restoration of said impulsing relay to complete a locking circuit to said magnet, said last contacts opened in response to the complete operation of said armature and remaining open during oe restoration thereof.

5. In an automatic switch, an impulsing relay, a slow release relay, a stepping magnet, an operating circuit for said slow release relay including make contacts on said impulsing relay, an operating circuit for said magnet including make contacts on said slow release relay and break contacts on said impulsing relay, and a ire-energizing circuit for said impulsing relay including make contacts on said magnet, whereby pre-energization of said impulsing relay in response to the restoration thereof is delayed by the operate time of said magnet.

6. In an automatic switch, an impulsing relay, a holding relay, a stepping magnet, an operating circuit for said holding relay including make contacts on said impulsing relay, an operating circuit for said magnet including make contacts on said holding relay and break contacts on said impulsing relay, a pro-energizing circuit for said impulsing relay, a line connected to said impulsing relay over which a series of impulses are delivered thereto, each of said impulses at times being of insufficient duration to permit complete operation of said magnet by said impulsing relay, a locking circuit for said magnet, and circuit control. means operated in response to a partial operation of said magnet to close said locking circuit, said last means operated in re?v sponse to the complete operation of said magnet to open said locking circuit and to close said preenergizing circuit.

7. In an automatic switch, an impulsing relay a slow release relay, a stepping magnet, an op erating circuit for said slow release relay include ing make contacts on said impulsing relay, a holding circuit for said slow release relay including contacts controlled by said stepping magnet, an operating circuit for said magnet including break contacts on said impulsing relay and make contacts on said slow release relay, a locking circuit for said magnet including normally open contacts thereon which are closed in response to a partial operation thereof and opened in response to the complete operation thereof, said contacts in said holding circuit of said slow release relay controlled by said magnet to assist in maintaining said slow release relay operated during impulsing.

8. In an automatic switch, an impulsing relay, a slow release relay, a stepping magnet, an operating circuit for said slow release relay including make contacts on said impulsing relay, a first circuit for operating said magnet including break contacts on said impulsing relay and make con.- tacts on said slow release relay, a second circuit for pro-energizing said magnet includin make contacts on said slow release relay and break contacts on said magnet, said break contacts on said magnet closed in response to a partial res? toration thereof and maintained closed until completion of said first circuit for said magnet,

9. In an automatic switch, an impulsing relay, a slow release relay, a stepping magnet, anoperating circuit for said slow release relay including make contacts on said impulsing relay, an operating circuit for said stepping magnet including break contacts on said impulsing relay and make contacts on said slow release relay, a pre-energizing circuit for said impulsing relay, a line connected to said impulsing relay over which a series of impulses are delivered thereto, each of said impulses at times being of insuflicient duration to permit complete operation of said magnet by said impulsing relay, a locking circuit for said magnet including make contacts and other contacts, a snap switch, partial operation of said magnet operating said last make contacts to close said locking circuit, said snap switch actuated by complete operation of said magnet to operate said other contacts to open said locking circuit and to close said pro-energizing circuit, said pro-energizing circuit assisting in operating said impulsing relay and assisting in maintianing it operated durng the restoring time of said magnet.

CLARENCE E. LOMAX.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,006,35i Hovland July 2, 1.935 2,242,397 Kater May 20, 1941 2,320,258 Bohman May 25, 1943 

